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dekker.one
1/* -*- mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*- */
2/*
3 * Main authors:
4 * Guido Tack <tack@gecode.org>
5 *
6 * Copyright:
7 * Guido Tack, 2004
8 *
9 * This file is part of Gecode, the generic constraint
10 * development environment:
11 * http://www.gecode.org
12 *
13 * Permission is hereby granted, free of charge, to any person obtaining
14 * a copy of this software and associated documentation files (the
15 * "Software"), to deal in the Software without restriction, including
16 * without limitation the rights to use, copy, modify, merge, publish,
17 * distribute, sublicense, and/or sell copies of the Software, and to
18 * permit persons to whom the Software is furnished to do so, subject to
19 * the following conditions:
20 *
21 * The above copyright notice and this permission notice shall be
22 * included in all copies or substantial portions of the Software.
23 *
24 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
25 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
26 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
27 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
28 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
29 * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
30 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
31 *
32 */
33
34#include <gecode/set/distinct.hh>
35
36/*
37 * These propagators implement the scheme discussed in
38 *
39 * Andrew Sadler and Carment Gervet: Global Reasoning on Sets.
40 * FORMUL'01 workshop in conjunction with CP 2001.
41 *
42 * Todo: make the propagators incremental.
43 */
44
45namespace Gecode { namespace Set { namespace Distinct {
46
47 /*
48 * "AtMostOneIntersection" propagator
49 *
50 */
51
52 Actor*
53 AtmostOne::copy(Space& home) {
54 return new (home) AtmostOne(home,*this);
55 }
56
57 ExecStatus
58 AtmostOne::propagate(Space& home, const ModEventDelta&) {
59 Region r;
60 LubRanges<SetView>* lubs = r.alloc<LubRanges<SetView> >(x.size());
61 for (int i = x.size(); i--; ) {
62 lubs[i].init(x[i]);
63 }
64 Iter::Ranges::NaryUnion bigT(r, lubs, x.size());
65
66 Iter::Ranges::ToValues<Iter::Ranges::NaryUnion>
67 as(bigT);
68
69 while (as()) {
70 int a = as.val(); ++as;
71
72 // cardSa is the number of sets that contain a in the glb
73 int cardSa = 0;
74 for (int i=x.size(); i--;)
75 if (x[i].contains(a))
76 cardSa++;
77
78 // bigTa is the union of all lubs that contain a
79 GLBndSet bigTa(home);
80 for (int i=x.size(); i--;) {
81 if (!x[i].notContains(a)) {
82 LubRanges<SetView> xilub(x[i]);
83 bigTa.includeI(home, xilub);
84 }
85 }
86
87 // maxa is the maximum number of sets that can contain a
88 int maxa = static_cast<int>((bigTa.size() - 1) / (c - 1));
89 bigTa.dispose(home);
90
91 // Conditional Rule A:
92 // If more sets already contain a than allowed, fail.
93 if (maxa < cardSa)
94 return ES_FAILED;
95
96 if (maxa == cardSa) {
97 // Conditional Rule B:
98 // All a used up. All other sets (those that don't have a in their
99 // glb already) cannot contain a.
100 for (int i=x.size(); i--;) {
101 if (!x[i].contains(a)) {
102 GECODE_ME_CHECK(x[i].exclude(home, a));
103 }
104 }
105 } else {
106 LubRanges<SetView>* lubs2 = r.alloc<LubRanges<SetView> >(x.size());
107 for (int i = x.size(); i--; ) {
108 lubs2[i].init(x[i]);
109 }
110 Iter::Ranges::NaryUnion bigT2(r, lubs2, x.size());
111
112 GlbRanges<SetView>* glbs = r.alloc<GlbRanges<SetView> >(cardSa);
113 int count = 0;
114 for (int i=x.size(); i--; ) {
115 if (x[i].contains(a)) {
116 glbs[count].init(x[i]);
117 count++;
118 }
119 }
120 Iter::Ranges::NaryUnion glbsa(r, glbs, cardSa);
121 Iter::Ranges::Diff<Iter::Ranges::NaryUnion,
122 Iter::Ranges::NaryUnion> deltaA(bigT2, glbsa);
123 Iter::Ranges::Cache deltaAC(r,deltaA);
124 // deltaAC contains all elements that are not yet known to be
125 // in a set together with a.
126 // Formally: \cup_i lub(x_i) - \cup_i {glb(s_i) | a\in glb(s_i)}
127
128
129 if (Iter::Ranges::size(deltaAC) == c - 1) {
130 // Conditional Rule C:
131 // If deltaA has exactly c-1 elements, all sets that are not yet
132 // known to contain a cannot contain a if it is impossible that
133 // they contain all of deltaA. Or the other way around:
134 // If a is added to the glb of a set s, deltaA must be a subset of
135 // s, because otherwise s would share at least one more element
136 // with another set that has a in its lower bound.
137 // Weird, eh?
138 for (int i=x.size(); i--; ) {
139 if (!x[i].contains(a) && !x[i].notContains(a)) {
140 deltaAC.reset();
141 LubRanges<SetView> xilub(x[i]);
142 if (!Iter::Ranges::subset(deltaAC, xilub)) {
143 GECODE_ME_CHECK(x[i].exclude(home, a));
144 }
145 }
146 }
147 }
148
149 }
150
151 }
152
153 return ES_NOFIX;
154 }
155
156}}}
157
158// STATISTICS: set-prop